Underwater mine

ABSTRACT

The invention relates to an underwater mine or decoy which should lie on the ocean bottom or which has buoyancy characteristics. The mine or decoy is made up of at least an expandable material and a foldable, preferably webbed shell which determines the external form of the mine. The disadvantages associated with the storage, transportation and stowage of heavy mines of fixed shape in submarines, small ships and aircraft are thereby avoided. It is possible to manufacture decoys or mines rapidly and economically, and they may have variable magnetic and/or sonar reflecting properties. The release of the decoys or mines from submerged submarines via forceful ejection is possible.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.07/537,128 filed Jun. 13, 1990, which is now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to an underwater mine or to an underwatermine decoy which should lie on the ocean bottom or which has buoyancycharacteristics.

Underwater mines customarily have a hard, normally ferromagnetic shell,among other things, in order to withstand the pressure in the oceandepths. They have, therefore, given sizes. Known, however, fromHightower, U.S. Pat. No. 4,953,465 is a flexible, inflatable minesuitable for use as a bottom mine for low depths and pressures. Alsoknown are underwater mines which can move or which have an outercovering which absorbs sonar signals.

SUMMARY AND OBJECTS OF THE INVENTION

It is therefore an object of the invention to eliminate the problemsassociated with the storage, transportation and stowage of mines offixed size and shape in submarines, small ships and aircraft. Further,it shall be economical, rapid and simple to deploy underwater minedecoys or, as the case may be, underwater mines. Further, it shall bepossible to deploy underwater mines or decoys with ferromagnetic orsonar-reflective properties which may be varied at the point of use toadapt to the local conditions, and the underwater laying of such mineswhile at high speed, e.g. from a submarine performing escape manoeuvres,or according to a predetermined minefield plan with a significantlyimproved relocating capability.

The foregoing objects are achieved by the present invention, whichprovides that the mine be constructed by using at least an expandablematerial and a foldable material, the final shape of the mine beingdetermined by the expansion of the expansion material and the expansionlimitations imposed by the outer shell. The only limitation on thefolding of the mine in preparation for release is that imposed by theexpandable materials, as well as those imposed by the other componentsof the mine as specified below. The advantage is the ease oftransporting a low volume mine or decoy, whose final form is onlyachieved after it has been released.

Further, the present invention achieves the foregoing objects by usingan expandable material which expands on contact with saltwater, andusing preferably a webbed material for the outer shell. The advantage isthat the mine requires no additional mechanism to achieve its finalform, and that the webbed external shell represents a simple, but a thesame time an extraordinarily strong element, which limits expansion ofthe expandable material, said material and said shell togetherdetermining the outer form. Mutsch et al., U.S. Pat. No. 4,123,974,describes the use of netting to restrain "to some extent" the plasticexplosive material while it assumes its natural shape on the ocean floorunder influence of water pressure and gravity.

Further, the present invention achieves the foregoing objects by usingsaid expandable material which expands due to a sudden pressuredifferential. The advantage is that a mine which is under enormouspressure, when forcefully released, will expand or inflate immediatelyto its final form.

Further, the present invention achieves the foregoing objects byemploying a steel, non-ferrous metal, or a plastic webbing material forthe outer shell. The advantage is that, depending on the webbing of theouter shell, the mine is more or less ferromagnetic or sonar-reflecting,can break up due to rusting or degeneration, possesses better explosioncharacteristics, etc. As a plastic material, Kevlar (Trademark DuPont)is preferred for its strength and long-term stability in storage. Toachieve better sonar-reflecting characteristics, the steel or nonferrousmetal wires in one or both directions of the webbing network can have amore or less concentrated mesh. The same holds true for Kevlar mesh, butthe fibers would be woven with sonar-reflecting substances such assilver thread.

Further, the present invention achieves the foregoing objects bydesigning the inside expanding material in such a manner that its finalfirmness under pressure corresponds to the water pressure, and the outershell surrounding said inside expanding material corresponds to theminimum expansion pressure of said inside material. The advantage isthat a mine can be selected from the available stock which isappropriate for the expected depth of the mission.

Further, the present invention achieves of the foregoing objects byemploying for said expandable material a mixture of expandable materialand explosive material. The advantage is that high explosive plastiquematerial can be partly mixed with other materials; the expansioncapability of the mixture with the expansion material is thereby notaffected; likewise the explosion capability of the explosive is notaffected when properly proportioned. If each mine or decoy is made up ofthis mixture, according to the present invention, the storage andtransportation of the mine is easier. Only when a detonator is providedis a raw mine an underwater mine. Whether homogeneously combined in themixture or placed within the expansion material in stripes or clumpform, the plastique needs only to be protected from saltwaterdeterioration for a limited time; modern silicone products areacceptable for this task, either as a protective covering or emulsifiedwith the constituents of the mixture. The use of pure plastiqueexplosives exposed to seawater in a bottom mine is disclosed in Mutschet al, U.S. Pat. No. 4,123,974.

Further, the present invention achieves the foregoing objects byemploying for said expandable material a mixture of expandable materialand iron powder, iron particles or a similar ferromagnetic material. Theadvantage is that a decoy can deceive a ferromagnetic detector. Ryan etal, U.S. Pat. No. 4,131,064, discloses a method of including foreignparticles, so-called tagging particles, with objects such as explosives.In the instant case, the tagging is magnetic, as it is desired that thedecoy be detected.

Further, the present invention achieves the foregoing objects byemploying for said expandable material a mixture of expandable materialand sonar reflecting material. The advantage is that a decoy can deceivea sonar detection device. Lengths of wide, flat, very thin silver ribboncan be used as a sonar-reflecting material within the mine.

Further, the present invention achieves the foregoing objects byemploying said expandable material and mixing it with a ferromagneticmaterial in such a manner that the mine exhibits a ferromagneticgradient from inside to outside. The advantage is that a decoy candeceive a detection device which can differentiate between types offerromagnetic mines. Steel balls are preferred for this application,since the density of ferromagnetic material is decisive and balls areeasy to handle.

Further, the present invention achieves the foregoing objects byemploying said expandable material and mixing it with a sonar-reflectingmaterial in such a manner that the mine exhibits a sonar transmissiongradient from inside to outside. The advantage is that a decoy candeceive a detection device which can differentiate between types ofsonar-reflecting mines. Silver ribbon with varying widths for therespective layers is a possible material. This method would render highspeed mine recognition, using sonar alone, almost impossible; slow speedverification after detection, using television, would most certainly benecessary, thus slowing the mine-sweeping process.

Further, the present invention achieves the foregoing by employing, forthe control of the various logical decisions within the mine, aprogrammable control device which is protected from the high waterpressure. The advantage is that the role of the central controller forall logical functions of the mine can be a standard device, which is apart of each mine and decoy. This eases the problem of stocking, andonly a specific part of the programming must be performed before themine is released. In the military arsenals alone there are hundreds ofdifferent types of miniature, programmable controllers which would meetthe requirements of the mine controller; a suitable controller can befound is smart land mines.

Further, the present invention achieves the foregoing objects byemploying a device with a detonator and a detonation controller incombination with an amount of ferromagnetic and/or sonar reflectingmaterial within the mine. The advantage is that after a pre-definedevent, the device discharges the above mentioned material under veryhigh pressure, so that the material partly mixes with the remainingmaterial of the mine or decoy and at least partly penetrates the outershell. This a required, due to international convention, in order tofind mines and dangerous decoys at some later time. Disclosed in Mutschet al., U.S. Pat. No. 4,123,974, are detonators of the type which couldbe used in the instant invention.

Further, the present invention achieves the foregoing objects bycombining in the mine a compressed air container, or similar device,with one or more expandable containers. The advantage is that after apre-defined event, the device releases the compressed air or gas in oneor more expansion chambers, whereby the mine may then change its formand, according to a pre-programmed scheme, may rise slowly or rapidly tothe surface. The disclosure of Holm, U.S. Pat. No. 3,084,627, describesa flotation method for mines for fixed form, whereby a bladder is usedto displace water within the mine; the method is equally applicable forthe instant invention.

Further, the present invention achieves the foregoing objects bycombining within the mine an ejectable heavy weight and a connectionbetween said weight and the rest of the mine. The advantage is thatafter a pre-defined event, the device releases the weight from the mine,or the weight is freed from the mine according to some other method. Thefreed mine is then free to rise to the end of a tether. The disclosureof Shimberg, U.S. Pat. No. 3,838,642, describes a method for releasingan external weight from a mine attached to it by a tether. Alsodescribed therein is a method for releasing the mine from the tetherafter some pre-defined event occurs.

Further, the present invention achieves the foregoing objects byemploying within the mine a foldable spring construction within acartridge or similar container, and whose unfolded form determines thefinal form of the mine. The advantage is that the spring constructionunfolds immediately after release of the mine or according to some othercriterium, e.g. after a pre-determined depth has been reached. Thisrepresents a very simple, economical underwater decoy; in its simplestform, it is made up of a sonar-reflecting shell of webbed plastic and asimple, folded spring construction.

An underwater mine or decoy, made up partly of formable material, isforcefully released from the hull of a submarine or a ship, or isotherwise released. This material expands under water according to apre-determined scheme and takes on a pre-determined form. Before beingejected, the mine can have a soft, relatively formless shape, in orderto easily put it into the ejection chamber and then under pressure.Methods of forceable ejection of decoys may be found in "NavyInternational", Submarine Signal & Decoy Ejector, Dec. 1990, page 483.In deep water, there exists an enormous pressure. The mine must be ableto expand, without bursting, and should preferably lie on the oceanbottom, either partly or fully under the sand or bottom debris. A light,webbed and very strong material, e.g. Kevlar (Trademark DuPont) orwebbed steel can be used as internal protection as well as for amulti-purpose skin or shell. The expansion of the formable material canbe triggered, for example, by contact with salt water. The quantity ofraw expandable material is determined by the expected depth where themine will be deployed. An example of expandable material acceptable foruse in saltwater is the bottled, highly compressed hard foam used in thebuilding trade. A further example is the use of synthetic cottonmaterials (such as Kapok, formally used in lifevests), such materialsbeing treated with silicones or similar coatings; they will expandslowly under heavy water pressure and will keep their shape until finalexpansion is complete and the mine has achieved its final form, afterwhich the fiber coating may very slowly disintegrate.

When the outer and inner pressures on the mine are equal, due toperforations or holes in the mine material, a very simple springconstruction, e.g. out of plastic and/or ferromagnetic material, couldgive the mine its final form. The spring construction is found within acartridge inside the mine and unfolds, for example, only after someseconds in salt water.

The mine material can be either sonar absorbent or reflecting,ferromagnetic (e.g. mixed with iron power) or not, and could possess asonar-transparent or a magnetic permeability gradient after the mineachieves its final form. Such gradients may be formed, for example, byemploying concentric shells of webbing inside of the outer shell of themine; inside the various snells would then be a different mixture ofexpandable material. Disclosed in Hightower, U.S. Pat. No. 4,953,465,are a number of methods for filling dry spaces within a sealedunderwater mine with hard foam, or alternatively with foam mixed withother materials, including weighty materials or materials which detonateand smoke. These methods may be applied to the mine of the instantinvention.

A mine whose expandable material is partly a mixture of plastiqueexplosive could, via intelligent logic as well as sensors, eitherself-destruct, or could act as a true mine and according to apre-programmed schemed either damage or destroy a ship or followingsubmarine, or could at least force the vessel to detour.

It is possible, but not absolutely necessary, to manufacture the minefrom a raw mine within a submerged submarine underway; the variableparts are the explosives and the detonator, the variable mixture andshells for creating the above mentioned gradients, the programmablelogic, etc. Finished mines from the available stock need only beprovided with the detonators, and the controllers must be programmed.Programming of the controllers is a fully automatic function; suchvariables as ocean depth, water temperature, depth of the submarine ifthe mine is to be released from a submerged submarine, etc. aretransmitted to the computer. Additionally, the type of threat expectedmay be manually keyed into the programmer, among other things in orderto set the sensitivity of the sensors. The captive torpedo in the U.S.military arsenal, the so-called Captor, is programmed in this manner aswell. The release or ejection mechanism is similar to that used insubmarines today to eject a wide variety of decoys, except that withinthe release chamber a high pressure may exist prior to release, in orderto increase the pressure on the mine and to insure its rapid expansionafter release. The cartridges of unexpanded roam or other expansionmaterial are placed with the explosives (in case the device is to be atrue mine and not a decoy) within the outer shell or within theconcentric shells in case the method of gradient building is desired,and the mine is placed in the expansion chamber. The mine is thencompressed, heated, or both, in order to allow said material to bereleased from said cartridges and to migrate somewhat within the shellor between the shells, as the case may be. On rapid expulsion of thisformless mine, for example the mine having the approximate form of asolid cylinder, the expansion material can expand freely between thelayers within its confinement space or spaces.

The mine can be fitted with a flotation capability. After somepre-programmed event, compressed air could be released from one vesselinto an expanding part of the mine or into a balloon, whereby the minecould charge its form or could float upwards with a pre-determinedspeed, either to the limits of a tether or to the surface. Depending onthe type of expansion capability of the air or gas container, the minecould repeat this maneuver. For example, a release valve would allow thegas to escape, would again be closed by the controller, and the ballooncould again be expanded by the gas.

Depending on the combination of materials used for the mine, the minecould have pre-defined buoyancy characteristics, whereby the mine, afterachieving its final form, could move away very slowly from its initialposition. For example, compressed cork granules within water solublecapsules would serve to force the mine slowly upwards. The number ofsaid capsules used would depend on the desired upward speed of the mine.

Other conventional and new mine elements, protected from the waterpressure, such as a microphone-on-a-chip, batteries, miniature sonardevices, transmitters for information transmissions, etc. can beemployed. An example of such mine elements can be found within thetorpedo described on pages 1370-1371 in the International DefenseReview, 12/1990. This is a so-called heavy weight torpedo and thus hassonar elements and processing units which, while miniaturized, are notof the miniature class envisioned for the mine of the present invention.High quality depth-finding devices sold commercially for private fishingboats could be very well adapted to the military role required by themine in this instant disclosure, and do roughly meet the foreseen sizeand power requirements of the mine or decoy. The new, commerciallyavailable microphone-on-a-chip for undersea use is not known, but theminiaturized device would be ideally suited for detecting sounds in thelow frequency spectrum of interest. In order to more easily locate amine at some later time, the mine could give a command, at somepre-determined time, to detonate a device within the mine which wouldexplosively distribute iron particles or similar material and/orsonar-reflecting material, which at least in part will penetrate theouter shell and mix with it. Such ragging of objects has been discussedabove and referenced to a previous U.S. patent.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a cross-sectional view through the approximate center of anexpanded mine at depth; only the left half is shown;

FIG. 2 a cross-sectional view of a mine similar to that of FIG. 1,illustrating a method of creating sonar reflecting gradients;

FIG. 3 illustrates a method of creating ferromagnetic gradients;

FIG. 4 shows a typical miniaturized controller with an aid for locatingthe mine at some future time;

FIG. 5 shows a method for allowing the mine to rise;

FIG. 6 illustrates attachment or a weight mechanism to a flexible mine;

FIG. 7 illustrates an economical, sonar-reflecting decoy; and

FIG. 8 illustrates an anti-torpedo curtain based on the principles ofthe instant underwater mine.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1 illustrates an embodiment of a mine or decoy made up ofconcentric shells or containers showing sonar-reflecting gradient layersbetween the shells; the mine is in its expanded form underwater. In thefigure, the mine has an outer shell 1 giving the mine its final shape inits completely expanded position under the influence of water pressure.The sections 2 through 6 represent concentric spaces filled withexpansion material (and optionally mixed with plastique explosivematerial as well), these sections being kept in their relative positionsby the concentric shells 7. The makeup of the material within thesespaces exhibits a monotonic increasing proportion of sonar reflectingmaterial from layers 2 through 6, whereby layer 6 has the greatestproportion of said material. The concentric shells of Kevlar 7 serve tocontain the expansion pressure of said expansion material. In one of thepossible embodiments, the space 8 at the approximate center of the mineillustrates the electronic control logic and detonator, as well as anyweight necessary to counteract buoyancy of the mine. Since this controlunit is small, may be shaped round, and as stated above must withstandextreme water pressure, it may be pressed out or ejected under pressurefrom the releasing vessel. In other embodiments of the mine, the weightmay be ejectable and would thus occupy a position on or near the skin ofthe outer shell 1 (see the above reference to U.S. Pat. No. 3,838,642for methods of storing and releasing a weight from a mine.) FIG. 1 islikewise illustrative of a mine exhibiting sonar-reflective orferromagnetic gradient characteristics, said gradients occupying thespaces 2 through 6, respectively, as in the above example.

Spies et al, U.S. Pat. No. 4,838,166 discloses a method for protectingexplosive charges by the use of several dissimilar layers of surroundingmaterial. Although not applicable to the instant disclosure, it doesindicate the method of using layers with different shock waveimpedances; in the instant invention, the analog is the use of multiplelayers with varying impedances, for example sonar-reflecting gradient,which is useful for deceiving an enemy at the location where mining isto be expected. This cross-sectional view is similar to the mine shownin FIG. 2, but only four concentric gradients 9, 10, 11 and 12 areillustrated for the mine with outer shell 1. As can be seen, thesonar-reflecting gradient with narrow, short strips of silver ribbon 13is the outer concentric layer 9, which reflects sonar signal with theweakest echo. The inner concentric layer 12 contains wide, long stripsor silver ribbon 16 and reflects sonar signals with the strongest echo.Layers 10 and 11, with increasing widths and lengths of silver strips 14and 15, respectively, reflect sonar signals more strongly than layer 9but less than layer 12; the echo from layer 11 is greater than fromlayer 10. The control logic and detonator in space 8 is as illustratedin FIG. 1 and of the type already described above. The expansionmaterial is not shown in the figure, but its existence within theconcentric layers keeps silver strips in their relative positions withintheir layer and therefore within the mine.

FIG. 3 illustrates one of the methods for creating a mine withferromagnetic gradients from inside to outside, which is useful fordeceiving an enemy. This cross-sectional view is similar to the mineshown in FIG. 2, but only three concentric gradients 17, 18 and 19 areillustrated for the mine with outer shell 1 and the control logic anddetonator in space 8. Concentric layer 17 contains the greatestconcentration of steel balls 20 within a small volume. Concentric layer18 has a very much greater cross-section than layer 17, but a smallerconcentration of steel balls and therefore could be interpreted falselyby a detection device. The outer concentric layer 19 has an even smallerconcentration of balls, but the first moment about the center centrum isgreat, which could lead to a false conclusion by a detection device.

FIG. 4 illustrates a mine in its expanded state, with a mixture ofexpansion material and explosives 26 within the shell 1 and the controllogic and detonator 8 in the approximate center of the mine. The figureillustrates the position of the programmable control device 21, adetonator 22 and detonation controller 23, ferromagnetic material 24,and a replaceable battery 25 within the unit 8; electrical connectionsare not shown in the figure. Within the spherical volume 27 are softiron filings, which may have an optimal sonar-reflecting form, whichwill penetrate the expansion material after detonation of the detonator22, which fills the spherical space between the space 27 and thespherical logic space 28 with the controllers 21 and 23. Detonation iscontrolled by a detonation controller 23, which is only necessary,according to international convention, for those mines which are truemines are not decoys. Controller 21, and controller 23 if it isavailable, are programmed via a control computer of the releasing vesselor aircraft prior to release of the mine.

FIG. 5 illustrates a method for allowing the mine to rise. A compressedair container 29 is loosely attached to the mine shell 1 via the valve31 and its actuator 30. Surrounding the valve is an expansion b-adder32, firmly attached to the mine shell 1 at the position shown. When theactuator 30 receives the signal from the controller 21 which isillustrated in FIG. 4 within the control logic of space 8, it opens thevalve 31 and allows the bladder to fill with the compressed air. After apre-programmed time, the actuator may receive a command from thecontroller 21 to close the valve. This operation may be repeated by thecontroller.

FIG. 6 illustrates the use of a tethered weight 33 within a casing 34attached to the mine in order to allow the mine to rise to apre-determined depth. When a current is applied to the release mechanism35, the weight 33 is free to drop out of its casing. If the mine is nowenabled to rise, as illustrated and described above in the FIG. 5description, the weight will remain stationary and the coiled tether 36will pay out until it reaches its end or limit, or until the controllerwithin the logic space 8 commands the breaking mechanism to stop theascent, i.e. by removing the current. This combined releasing andbreaking mechanism is a simple solonoid-controlled device; stop andspeed control mechanism, as well as advice for combining them, are to befound in "Product Engineering Design Manual", Greenwood (McGraw-Hill),Chapter 10, as well as in numerous mechanical engineering and hobbymanuals.

FIG. 7 shows a very simple mine embodiment which makes it ideal as aneconomical decoy. The outer mine shell 1, with Kevlar webbing 37 wovenwith silver thread 38 and/or ribbon 39 in order to reflect sonarsignals, is in a collapsible form until released, after which it expandsdue to the expansion of the telescopic spring elements 41 of theexpansion device 40. Only the decoy in its fully expanded form is shown.Since the shell 1 is made of relatively course webbing, there is no needto compensate for water pressure from outside or expansion pressuresfrom expansion materials inside the shell, and the speed of expansion isimmaterial. The expansion device 40 may contain folding elements as inan automatic opening umbrella, or other spring-loaded telescopingdevices, such as self-adjusting bookshelf bookends, welded together andadapted to the instant application and shown in the figure. Othermethods of expansion include the use of clock-springs, which need onlybe extracted from their restraining rings, after which they expand inthe general form of a ball of tangled spring, thus forcing the shell 1into a cylindrical form; such a tangle of spring ribbon would tend toconfuse a sonar detector, thus causing a loss of time in the mineclearing process. The expansion device 40, many of which may be used butonly shown singularly in the figure, has telescoping expansion elements41, spring-loaded by coiled springs (not shown), and whose padded ends42 push the skin of the shell 1 out to the desired shape after theexpansion. At release and before expansion, the elements are held intheir collapsed position by water soluble latches, which dissolve inseawater and allow expansion of the elements 41.

The form of the mine is not limited to the closed form described above.For example, FIG. 8 illustrates a compressed anti-torpedo curtain 43which could be released by a submerged submarine on detection of athreatening torpedo. The curtain could have the closed form describedabove, in a relatively flat embodiment; it may also be a simple sheet oftough webbed material 37, weighted on one or more edges with weights 44(four are shown) and buoyed with expansion flotation elements 45 on theother edges. After ejection underwater, the curtain would achieve a moreor less vertical orientation at the position and time calculated by thesubmarine's data processing system. A leaf spring construction 47 with aplurality of unfoldable elements 48, connected by joints 49, andactuating springs 50, serves to rapidly expand the curtain immediatelyafter ejection. The extremeties of the arms are attached to theperiphery of the curtain at points 51. After the curtain's electroniccontrollers with sensors 46 (three are shown in the figure) havedetected impact as measured by the accelerometers mentioned below, theedge flotation elements 45 would then be inflated rapidly to create aseries of sea anchors at the periphery of the curtain, thus in effectcapturing the torpedo or rendering it harmless to the submarine. Notshown is the collapsed form of the sea anchor or the expanded form,which when opened would resemble the nylon sea anchors typically usedfor small motor boats. The three sensors 46 and their associatedcontrollers, batteries and wires to the flotation elements are likewisenot illustrated in detail; typical ultraminiature controllers in themilitary arsenal have been mentioned above, while the motion sensorsused to detect impact may be of the Type 3021-020-P micro-mechanicalaccelerometer from the company IC Sensors, or its equivalent from LittonIndustries, Inc. The decentralized controllers are gang-programmed bythe submarine control system shortly before release; the fine cables forthis purpose, severed at launch, are not illustrated. Also not shown isthe release mechanism for the sea anchor, since only release and nopowered expulsion is necessary; for this purpose, retaining and lockingdetents and similar locking and releasing mechanisms may be found in"Mechanisms, Linkages, and Mechanical Controls", Chapter 12, Chironis,McGraw-Hill as well as in numerous other mechanical engineering andhobby manuals.

Although the expandable materials and their expansion mechanisms, thematerial for the outer shell and the internal strengthening andcontainers, and explosives nave been described according to the knownstate of the art, the invention is not limited to these materials, andnew or improved materials and processes may be used in the futureaccording to the teachings of the present invention. In particular,future expansion materials exhibiting very low buoyancy characteristicswould serve to reduce the required counterweighting.

What is claimed is:
 1. Underwater mine decoy, characterized by anexpandable material and an outer shell formed by a webbed foldablematerial, the final shape of the mine decoy being determined by thelimitations imposed by the outer shell.
 2. Underwater mine decoyaccording to claim 1, characterized by using an expandable materialwhich expands on contact with saltwater.
 3. Underwater mine decoyaccording to claim 1, characterized by using said expandable materialwhich expands due to a sudden pressure differential.
 4. Underwater minedecoy according to claim 1, wherein the outer shell material is formedof one of steel, non-ferrous metal or plastic webbing material. 5.Underwater mine decoy according to claim 1, characterized by employingfor said expandable material a mixture of expandable material and anentrained explosive material.
 6. Underwater mine decoy according toclaim 1, characterized by employing for said expandable material amixture of expandable material and entrained iron powder, iron particlesor a similar ferromagnetic material.
 7. Underwater mine decoy accordingto claim 1, characterized by employing for said expandable material amixture of expandable material and entrained sonar reflecting material.8. Underwater mine decoy according to claim 1, characterized byemploying said expandable material mixed with a ferromagnetic materialsuch that the mine decoy exhibits a ferromagnetic gradient. 9.Underwater mine decoy according to claim 1, characterized by employingsaid expandable material mixed with one of sonar reflecting material andferromagnetic material such that the mine decoy exhibits a sonartransmission gradient or a ferromagnetic gradient, respectively, saidgradient being created by employing a plurality of concentric shellswithin said outer shell, and employing a varying amount of saidferromagnetic and/or said reflecting material in the expandable materialbetween said shells.
 10. Underwater mine decoy according to claim 1,characterized by employing a programmable control device containedwithin the outer shell which is constructed to withstand high waterpressure and which controls the various logical decisions within themine decoy.
 11. Underwater mine decoy according to claim 1,characterized by employing a device contained within the outer shellwhich has a detonator and a detonation controller in combination with anexplosive material and an amount of ferromagnetic and/or sonarreflecting material within the mine to facilitate relocation of themine.
 12. Underwater mine decoy according to claim 1, furthercharacterized by an explosive material contained within the outer shell.13. Underwater mine decoy according to claim 12, characterized by usinga detonator and a detonation controller connected to the explosivematerial within the mine.